Slotted skid plates are used with concrete saws to cut concrete before it is hardened to the green stage. This is described in U.S. Pat. No. 4,769,201. But the concrete is very abrasive. Thus, the skid plates are made of steel to resist the wear from sliding over the concrete surface and to resist the wear from the abrasive concrete carried by the blade at the cutting edge and which widens the slot in the skid plate. The skid plates were made of sheet steel and bent to the desired shape. But the steel skid plates warp during manufacture and use and that causes raveling as the cut concrete grooves ravel unless the skid plates are flat against the concrete during cutting. There is thus a need for an improved skid plate that remains flat against the concrete after manufacture and during use.
One patent addresses this problem of the non-flat skid plates by using a truss to warp the skid plate into a desired configuration, as described in U.S. Pat. Nos. 5,507,273. But adjusting the truss and fixing the truss to lock in the desire distortion is complex and time consuming. Indeed, it is so difficult that special equipment and methods are used, as described in U.S. Pat. No. 5,689,072. There is thus a need for a better way to achieve a flat skid plate during cutting. A less expensive way to make skid plates is also desirable.
The skid plates are fastened to the saw by inserting pins through holes in the distal ends of spring loaded pistons The pistons resiliently urge the skid plate against the concrete surface during cutting. Because the alignment of the skid plate with the saw blade affects the quality of the groove cut in the concrete, the pins holding the skid plate to the saw have a very tight fit with the mating holes in the pistons. But removing the pins is difficult because the pins often freeze in place. The skid plates thus become difficult to remove and that encourages workers to leave them as long as possible, and often too long. Unfortunately, the skid plates wear, sometimes after as little as 1200 feet of cutting and the quality of the cut groove deteriorates with the wear. There is thus a need for a better way to fasten the skid plate to the saw and to make it easy to remove a used skid plate from the saw and to fasten a replacement skid plate to the saw.
There is a close fit between the cutting blade and the slot in the skid plate through which the blade extends during cutting. The concrete is very abrasive and during operation of these early-entry concrete saws that use up-cutting blades, the portion of the skid plate immediately adjacent the cutting edge of the rotating cutting blade wears away much faster than the remaining portion of the skid plate. The result is a widening of the slot adjacent the cutting edge of the blade. As the width of the slot in the skid plate increases, the quality of the cut in the concrete decreases. Thus, a skid plate may product unacceptable cuts because the leading edge of the slot widens unacceptably from use, and has to be discarded. One way to address this excessive wear is discussed in U.S. Pat. No. 4,903,680, but the mechanism described in that patent requires many moving parts and is limited by the sheet-metal skid plate which is sensitive to distortion from thermal or mechanical forces. There is thus a need for an improved way to resolve the wear at the leading end of the slot.